JPH027678A - Contour compensation circuit - Google Patents

Abstract

PURPOSE:To obtain a uniform high resolution characteristic by providing a contour compensation characteristic decision circuit varying the compensation characteristic depending on a position on the screen or a lens parameter and a variable compensation circuit applying resolution compensation calculation to a video signal input by the output of the said decision circuit. CONSTITUTION:The title circuit consists of the contour compensation characteristic decision circuit 1 and the compensation characteristic variable contour compensation circuit 2. The contour compensation characteristic decision circuit 1 obtains an input of screen position information and lens parameter information to decide compensation and to output a compensation data. The variable compensation circuit applies compensation calculation with respect to a video signal input according to the output command to obtain a video signal output with high resolution. Then the compensation characteristic is adjusted so as to make the resolution characteristic varied depending on the lens parameter and the position of the screen high uniformly. Thus, a television signal having uniformly high resolution is always obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a contour compensation circuit for a television camera device, and in particular, the contour compensation circuit changes depending on parameters such as the aperture value, focal length, and subject distance of the imaging lens, and the position within the screen. The present invention relates to a contour compensation circuit that compensates for the resolution characteristics of the image and always obtains a video signal with excellent resolution.

[Conventional technology]

Currently, television cameras are widely used as devices for obtaining television signals. A television camera uses an optical lens to form an optical image of a subject on an image pickup tube or a light-receiving surface of a solid-state image sensor, and converts this optical image into an electrical signal to obtain a television signal.

As an index representing the fineness of the image that can be resolved by the above-mentioned imaging lens, imaging tube, and solid-state imaging device, -
(Modulation Transfer Fun
ction) is used. Therefore, resolution characteristics will also be referred to as MTF characteristics hereinafter. The MTF characteristic represents a two-dimensional frequency response, and represents a change in contrast with respect to a pattern in which brightness changes sinusoidally. FIG. 4 shows an example of MTF characteristics of a general imaging lens. The horizontal axis is spatial frequency, and the vertical axis is contrast (response). The higher the spatial frequency, the smaller the MTF. This means that fine patterns lose their contrast and cannot be resolved. Furthermore, in television camera equipment, in addition to the lens, the image sensor also uses high-frequency MTF.
is known to decrease. For this reason, television camera apparatuses in practical use are equipped with a contour compensation circuit for compensating for the drop in MTF in the high range, as shown in FIG. The configuration of this contour compensation circuit is 1. For example, there is a broadband contour compensation circuit described in the NHK Giken Monthly Report, October 1973 issue.As described in this document, the conventional contour compensation circuit always has a constant Therefore, conventional contour compensation has the following problems, which need to be solved.

[Problem to be solved by the invention]

Figure 5 shows an example of the MTF characteristics of the imaging lens in detail.
Problems with conventional contour compensation circuits will be explained.

Figure 5 (A) is on the optical axis (center) of the lens and 81 from the optical axis.
The MTF characteristics at the nilIIi point are shown. On a 1-inch light receiving surface, the 8nnii point is at the periphery of the screen.The aperture value (hereinafter referred to as F value) and focal length f are the same, but the MTF at the periphery is lower than the MTF at the center. .

The decrease is particularly significant at high spatial frequencies. FIG. 5(B) is a diagram showing the change in MTF depending on the F value of the lens, and FIG. 5(C) is a diagram showing the change in MTF depending on the focal length f of the lens.

FIG. 5(8) shows the MTF measured at the center of the lens at a focal length f=12 m++, and the MTF characteristics change depending on the F value. FIG. 5(C) shows the MTF measured at the center of the screen with an F value of 1.8. MTF also depends on focal length f
It can be seen that the changes. Although not shown in the figure, it is known that the MTF changes depending on the distance L to the subject. As described above, the MTF characteristics of the imaging lens change depending on the lens parameters such as the F value, focal length f, and subject distance of the lens, and the position such as the center and periphery of the screen.

However, conventional contour compensation circuits perform contour compensation in a similar manner to the entire screen. Further, the amount of compensation is not adjusted according to the lens parameters.

Therefore, the obtained television signal is directly affected by changes in the MTF of the lens, and it is not always possible to obtain a high-resolution signal.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned disadvantages and provide a contour compensation circuit that can always obtain high resolution characteristics even when the screen position or the parameters of the imaging lens change.

[Means to solve the problem]

In order to achieve the above object, the present invention takes the following measures.

1. Depending on the screen position or lens aperture value.

A contour compensation characteristic determining circuit that varies the compensation characteristic depending on lens parameters such as focal length and object distance, and an output of the contour compensation characteristic determining circuit performs M image degree compensation calculation on the video signal input and outputs the video signal. It was decided to provide a variable compensation circuit to obtain a variable compensation circuit. I also did the following to implement this:

2. The contour compensation characteristic determination circuit that makes the compensation characteristic variable in the above item 1 includes means for storing in advance resolution characteristics that change depending on the screen position or lens parameters, and input of screen position information and lens parameter information. The present invention has a means for obtaining a resolution characteristic corresponding to the input information, a means for determining a compensation characteristic from the resolution characteristic, and a means for outputting an emphasis frequency and a compensation amount for obtaining the compensation characteristic.

3. In addition, the contour compensation characteristic determining circuit that makes the compensation characteristic variable in the above-mentioned item 1 stores or calculates the compensation characteristic for compensating the resolution in accordance with the combination conditions of the screen position and lens parameters, and stores or calculates the compensation characteristic for compensating the resolution, The present invention has means for outputting an emphasis frequency and a compensation amount for compensation based on input information.

The drawings will be explained later, but the means in item 1 corresponds to FIG. 1, the means in item 2 corresponds to FIG.
The items in the section correspond to FIG.

[For production]

Among the means described in item 1 above, the contour compensation characteristic determination circuit that makes the compensation characteristic variable determines the amount of compensation to compensate for the resolution that varies depending on the screen position and lens parameters to a uniform high resolution on the screen, and performs compensation. This is output as quantitative data. Further, the variable compensation circuit performs compensation calculations on the video signal in response to an instruction to output the compensation amount data.

In the contour compensation characteristic determining circuit according to the means of item 2 above,
The means for pre-storing resolution characteristics that change depending on the screen position and lens parameters stores resolution characteristics that are unique to devices such as imaging lenses and imaging elements. The means for obtaining the resolution characteristics corresponding to the input information obtains the resolution characteristics corresponding to the screen position information and lens parameter information in the photographing state from the resolution characteristics uniquely determined by the apparatus, and outputs this information. The means for determining the compensation characteristic determines the compensation characteristic to obtain uniform high resolution on the screen from the information on the resolution characteristic. The means for outputting the emphasis frequency and the compensation amount outputs compensation amount data to be given to the video signal in order to have the thus determined compensation characteristics on the screen.

The contour compensation characteristic determination circuit according to the means in item 3 above stores in advance compensation characteristics corresponding to resolution characteristics for various combinations of screen positions and lens parameters that may occur in the shooting state, based on the resolution characteristics determined uniquely to the device. This is either stored in advance or calculated and obtained, and from this compensation characteristic, necessary compensation amount data regarding the emphasis frequency and compensation amount for compensation is output based on the input information of the photographing state.

As a result of the above, for example, when the resolution around the screen is significantly reduced, the resolution characteristics corresponding to spatial frequencies at the periphery are improved and the amount of compensation is increased to achieve high resolution. Furthermore, if the resolution decreases when the lens aperture is opened, the resolution characteristics are improved and the amount of compensation is increased so that the resolution becomes the same as when the lens is stopped down.

That is, the present invention makes it possible to adjust the compensation characteristics so that the resolution characteristics, which vary depending on the lens parameters and the position of the screen, can be made into a uniform high resolution. Therefore, according to the present invention, it is possible to obtain a television signal that is always uniform and has high resolution.

It should be noted that the above-described means in item 3 has the advantage that the circuit can be simplified by using a ROM memory or arithmetic means.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing one basic configuration of a contour compensation circuit according to the present invention. This circuit consists of a contour compensation characteristic determination circuit 1 and a variable compensation characteristic contour compensation circuit (hereinafter simply referred to as a variable compensation circuit).
Consists of 2. As shown in the figure, the contour compensation characteristic determining circuit (simply referred to as the compensation characteristic determining circuit) 1 receives input of screen position information and lens parameter information, determines the amount of compensation according to these information, and outputs compensation amount data. . In response to this output instruction, the variable compensation circuit performs compensation calculations on the video signal input and obtains a high resolution video signal output.

FIG. 2 is a diagram showing another basic configuration of the contour compensation circuit of the present invention. In particular, the contour compensation characteristic determining circuit 1 includes a means for pre-memorizing resolution characteristics uniquely determined by devices such as imaging lenses and image sensors, and a means for storing in advance resolution characteristics uniquely determined by devices such as imaging lenses and image sensors, and a means for storing in advance the resolution characteristics uniquely determined by devices such as imaging lenses and image sensors, and a means for storing in advance the resolution characteristics uniquely determined by devices such as imaging lenses and imaging elements, F, focal length f, subject distance L) and screen position information (
means for determining the resolution characteristic of a lens corresponding to the input information from the coordinates and means for outputting a compensation amount. This output is input to the variable compensation circuit 2.

FIG. 3 is a diagram showing another basic configuration of the contour compensation circuit of the present invention. The internal configuration and operation of the compensation characteristic determining circuit are different from those in FIG. That is, in FIG. 3, compensation characteristics corresponding to various combinations of screen positions and lens parameters are stored or calculated in advance, and the required emphasis frequency, This replaces the means for outputting the compensation amount. This has the advantage that the circuit is simpler than the one shown in FIG.

FIG. 6 shows a block diagram of a television camera device using the above-mentioned contour compensation circuit. First, the configuration of this camera will be explained, and then the operation will be explained. This camera device includes an imaging lens 10, a color separation prism 26° and an imaging tube 11, 12, 13.
．． Amplifier circuit 14.15.16. Variable compensation circuit 17.18
．． 19, compensation characteristic determination circuit 24, lens parameter detection circuit 20, synchronization signal generation circuit 22, screen position detection circuit 2
3 and a process circuit 25. Note that camera circuits that are not directly related to the gist of the present invention are omitted.

The imaging lens 10 converts the optical image of the subject into a color separation prism 2G.
The image is formed through the image pickup tube 11 and I2.13. Image tube 1
1 photoelectrically converts images of red light (R), image pickup tube 12 uses green light (G), and image pickup tube 13 uses blue light CB), and outputs signals corresponding to the colors of the objects. Since the signal obtained as described above passes through the imaging lens 10, the color separation prism 26, and the imaging tube, the MTF of high spatial frequencies is reduced. Image tube 1
The output signals of 1.12.13 are sent to the amplifier circuit 14.1, respectively.
5.16, the signal is amplified to a predetermined level, and then input to variable compensation circuits 17, 18, and 19. Variable compensation circuit 1
7.18.19 compensates for a video signal with reduced MTF and converts it into a signal with high resolution. A method for determining this compensation characteristic and a compensation method will be described later. The compensated video signal is subjected to, for example, NTSC color signal processing by the processing circuit 25.

Next, a method for determining compensation characteristics will be explained. In the television camera apparatus shown in FIG. 6, a lens parameter detection circuit 20 detects the F value, focal length f, and subject distance of the lens. This detection is obtained by detecting the position of each lens constituting the imaging lens using, for example, a potentiometer, a rotary encoder, or the like. The screen position information detection circuit 23 detects the current scanning position from the synchronization signal. To detect the scanning position, for example, a counter that is reset by a vertical synchronization signal and a counter that is reset by a horizontal synchronization signal are used. By counting the number of horizontal synchronization signals and the number of clocks using these counters, the X and Y coordinates of the scanning position can be determined. The lens parameter information and screen position information obtained as described above are input to the compensation characteristic determining circuit 24.

The compensation characteristic determining circuit 24 receives input information (F, f, L,
The MTF characteristic of the lens is determined from (X, Y), and a signal to compensate for this is generated. For example, the horizontal MTF characteristic is the 7th
If the solid line in Figure A is used, the compensation characteristic will be as shown in the dotted line in Figure 7B. The compensated MTF characteristic is as shown by the dashed-dotted line in FIG. 7C. Note that the reason why the characteristic after compensation is a downward characteristic in the high frequency range is to prevent noise in an unnecessary band from being mixed into the video signal. Further, FIG. 7C is an example of the compensation characteristic, and it is even better if it is determined in accordance with the human visual characteristics.

FIG. 8 is a diagram showing a configuration example of a compensation characteristic determining circuit corresponding to FIG. 3. Lens parameter information (F, f, L)
and screen position information (x, y) are A/D converted and input to the compensation characteristic determination ROM. This compensation characteristic determining ROM contains F
, f, L and X.

Compensation characteristics are calculated and stored in advance according to various combination conditions regarding Y, and the compensation characteristics are outputted in accordance with the combination conditions of the input information of the photographing state.

FIG. 9 is a diagram showing a modification of FIG. 8. The difference between FIG. 9 and FIG. 8 is that an interpolation calculation circuit 39 is provided.In the configuration shown in FIG. Determine. According to this configuration, the ROM capacity is only required for representative data, and the amount of memory can be saved.

FIG. 1O shows another embodiment of the compensation characteristic determining circuit 24.

This figure is a diagram showing another configuration example corresponding to FIG. 3. The difference between this circuit and FIGS. 8 and 9 is that no ROM is used to determine the compensation characteristics.

In this circuit, MTF is determined by lens parameters and screen position.
The characteristics are approximated by a function, and a compensation signal is created using a function with the opposite characteristics.

FIG. 11 is a block diagram showing the configuration of the variable compensation circuit. This circuit includes a vertical contour compensation circuit 50 and a horizontal contour compensation circuit 5.
If starting from 1. The vertical contour compensation circuit is a circuit that delays a signal by an integral multiple of the horizontal scanning period (referred to as nH delay circuit) 52
．． 53. It consists of adder circuits 54 and 57, an inverter circuit 561, and a multiplier circuit 55. The configuration of the horizontal contour compensation circuit 51 is basically the same as that of the vertical contour compensation circuit 50, and minute time delay circuits 60 and 61 are used instead of the nH delay circuit.

The delay time of this minute time delay circuit will be described later.

The operation of the variable compensation circuit will be briefly explained. Since the operating principle is the same in both the vertical and horizontal directions, the operation of the horizontal contour compensation circuit 51 will be discussed here. FIG. 12 shows the horizontal contour compensation circuit. Note that the same reference numerals as in FIG. 11 are used. If the input signal to the horizontal contour compensation circuit 51 is f (t) and the delay time of the minute time delay circuit is τ, the output signal of the minute time delay circuit 60 is f (at t-), and the output of the minute time delay circuit 61 is f (by -2). In this horizontal contour compensation circuit 51, the input signal f (t) and the signal f (at t-2) of the minute time delay circuit 61 delayed by 2 are added to the addition circuit 51.
Add by 2. The output of this adder circuit 62 is fD)+fD-2)...(1). The amplitude of this signal is reduced by half by a multiplier circuit 63, and the polarity is further inverted by an inverter circuit 64. This signal and the output signal f (-τ) of the minute time delay circuit 60 are added by an adder circuit 65.

As a result, the output signal Eh of the adder circuit 65 is as follows.

Below margin Eh=f (-τ)-2(f (t) +f (t-
2τ))... (2) Here, considering the input signal f(t) as a sine wave, f(
t) = sin ω
−= −(3), then the characteristic E of the compensation signal is
h is Eh=sinω(t-τ) −−(sinω+sin
ω(t-2r) )=(1-cosωτ) X5inω
(at t-) ......(4) becomes the comb-shaped characteristic. This compensation signal is multiplied by a certain coefficient k and added to the output signal f D ) = sin ω (with −) of the minute time delay circuit 59 . The resulting signal f'(t) is f'(t) = sir+ω(t-r) +k(1-co
sωv) X5inω(t-t)= (1+k(1-
CO3(11τ) ) X5inω(t-r)...
...(5) becomes. It can be seen from equation (5) that the amount of contour compensation can be adjusted by changing k. Also, since the frequency characteristic C(τ) of the horizontal contour compensation circuit is C(τ) = 1+k (1-cosωτ),
The emphasized peak frequency ω, is obtained by differentiating the above equation and finding it from the maximum point: ω, = mπ/τ (m = 1.2.3...)
becomes. Actually, the frequency of m=1 becomes the emphasis frequency.

As described above, various contour compensation characteristics can be realized by changing k and τ. FIG. 13 shows an example of compensation characteristics. Fig. 13(A) shows the case where k is changed; Fig. 13(B)
) is the compensation characteristic when the delay time τ is changed. The above-described compensation characteristic determining circuit 24 outputs k and τ as compensation amounts corresponding to the lens parameters and screen position.

In the vertical contour compensation circuit 50, the delay time is one horizontal scanning period,
Or, since it is limited to an integer multiple thereof, the horizontal contour compensation circuit 5 described above except that the emphasis frequency is determined by the number of scanning lines.
Needless to say, the operation is the same as No. 1. As shown in FIG. 11, the output signal of the horizontal contour compensation circuit 51 is multiplied by a gain k, and the output signal of the vertical contour compensation circuit 50 is multiplied by a gain and added to the original signal. As explained above, the characteristics of the contour compensation circuit can be controlled by the delay times nH1 and τ, the gain, and . By selecting these parameters according to the MTF characteristics of the lens and image pickup tube,
Dimensional resolution compensation becomes possible. In Figure 11, nH
The delay circuit 68 and the minute time delay circuit 59 function to match the timings of the original signal and the compensation signal. This delay time is made the same as the delay time of the nH delay circuit 52 and the minute time delay circuit 60. Note that the connection order of the horizontal contour compensation circuit 51 and the vertical contour compensation circuit 50 may be reversed.

FIG. 14 shows another embodiment of the variable compensation circuit. In this circuit, a signal that passes through minute time delay circuits 70 and 71 and is delayed by a time of 2τ is input to a time delay circuit 72 (in IH-2). This signal is again delayed by 2τ period. Next, the signal is input to the delay circuit 75 of (IH-2τ) in the same manner as above. Furthermore, this output is also delayed by a period of 2. Each output of the delay circuit configured as described above is connected to the gain adjustment circuits 78 to 78, respectively.
The gain is adjusted by 86 and input to the adder circuit 87 all together. A resolution-compensated signal is obtained from the output terminal of the adder circuit 87. When the above processing is considered on the screen, it is nothing but spatial convolution filtering processing using a 3×3 mask. A resolution compensation filter can be configured by controlling the coefficients of the filter, that is, the gains of the gain adjustment circuits 78 to 86. FIG. 15 is a diagram showing an example of a spatial filter. FIG. 15(A) is an example of a filter that outputs the original signal as it is, and FIG. 15(B) is an example of a filter that emphasizes high frequencies. The coefficients shown in FIG. 15(A) are used in the center of the lens and in areas where resolution compensation is not required, and the coefficients shown in FIG. 15(B) are used in areas where resolution compensation is required. Of course, it goes without saying that the uniformity of resolution can be increased by appropriately selecting filter coefficients depending on the screen position and lens parameters. Also, the size of the filter is 3×
The size is not limited to 3, and may be even larger.

In this example, the F value, focal length f, and subject distance were used as lens parameters, and X and Y were used as position information.
Contour compensation may be performed using only some main parameters. Further, although it is not as effective as performing compensation in both the horizontal and vertical directions, the circuit can be simplified by performing compensation only in either the horizontal or vertical direction.

In the above embodiments, the method of compensating for changes in MTF due to lenses has been mainly explained. However, MT depending on the screen position
It is known that changes in F occur not only in lenses but also in image pickup tubes. Therefore, it is easy to understand that even better resolution characteristics can be obtained by performing contour compensation in consideration of the MTF characteristics of the image pickup tube. Furthermore, although the embodiments have been described with reference to an image pickup tube type camera, it goes without saying that the single contour compensation circuit can also be applied to a television camera using a solid-state image pickup device. Furthermore, it is clear that the present compensation method is effective in both analog processing and digital processing.

Note that one of the main points of the present invention is to adjust the compensation characteristics according to the screen position to obtain uniform resolution within the screen. This principle can be applied to the contour compensation circuit of a display device using, for example, a CRT (cathode ray emission display tube). It is known that in a CRT, the resolution at the periphery is lower than the resolution at the center. It is easy to understand that by adjusting the compensation characteristics according to the screen position, images with excellent resolution can be obtained in all display areas.

〔Effect of the invention〕

As described above, according to the present invention, even if the lens parameters and the screen position change, a similar MTF characteristic can be obtained, and a high-resolution signal can always be obtained, which is an excellent effect.

In addition, among the contour compensation characteristic determining circuits of the present invention, those having a basic configuration (shown in FIG. 3) in which the compensation characteristics are stored in advance or determined by calculation have the advantage that the circuit is simplified. .

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one basic configuration of the contour compensation circuit of the present invention, FIG. 2 is a diagram showing another basic configuration of the contour compensation circuit of the present invention, and FIG. 3 is a diagram showing one contour compensation circuit of the present invention. A diagram showing another basic configuration of. Figures 4 and 5 are diagrams showing the MTF characteristics of the lens, Figure 6 is a block diagram of a three-tube color camera using this contour compensation circuit, Figure 7 is a diagram showing the compensation characteristics, and Figure 8 is compensation FIG. 9 is a diagram showing a modification of FIG. 8; FIG. 10 is a diagram showing another embodiment of the compensation characteristic determining circuit;
Fig. 11 is a diagram showing the configuration of the variable compensation circuit, Fig. 12 is a diagram showing the configuration of the horizontal contour compensation circuit, Fig. 13 is a diagram showing an example of compensation characteristics, and Fig. 14 is a diagram showing another implementation of the variable compensation circuit. FIG. 15 is a diagram showing an example of a spatial filter for contour compensation. [Explanation of symbols] 1.24...Axis compensation characteristic determining circuit 2...Variable compensation circuit 10...Imaging lens 11.1
2.13... Image pickup tube 17.18.19... Variable compensation circuit 20... Lens parameter detection circuit 23... Screen position detection circuit 25... Process circuit

Claims (1)

[Claims] 1. In a contour compensation circuit that compensates for a decrease in resolution on a screen imaged by an imaging lens and an imaging tube or a solid-state imaging device, depending on the screen position or the lens aperture value,
A contour compensation characteristic determining circuit that makes the compensation characteristic variable depending on lens parameters such as focal length and object distance, and a variable circuit that performs resolution compensation calculation on the video signal input using the output of the contour compensation characteristic determining circuit to obtain the video signal output. A contour compensation circuit comprising a compensation circuit. 2. The contour compensation characteristic determining circuit for making the above-mentioned compensation characteristic variable includes a means for pre-memorizing resolution characteristics that change depending on the screen position or lens parameters, and a means for preliminarily storing resolution characteristics that change depending on the screen position or lens parameters, and adjusting the resolution characteristics by inputting the screen position information and lens parameter information. A patent characterized in that it has means for obtaining a resolution characteristic corresponding to information, means for determining a compensation characteristic from the resolution characteristic, and means for outputting an emphasis frequency and a compensation amount for obtaining the compensation characteristic. A contour compensation circuit according to claim 1. 3. The contour compensation characteristic determining circuit that makes the above compensation characteristic variable stores or calculates the compensation characteristic for compensating the resolution in accordance with the combination of screen position and lens parameters, and adjusts the screen position information and lens parameter information. 2. The contour compensation circuit according to claim 1, further comprising means for outputting an emphasized frequency and a compensation amount for compensation according to an input.